The present invention relates to a vascular prosthesis having self sealing capabilities and, more particularly, to vascular grafts fabricated from non-woven materials impregnated or coated with thrombogenic agents.
End-stage renal disease (ESRD) occurs when the kidneys are no longer able to function at a level that is necessary for day to day life. It usually occurs as chronic renal failure worsens to the point where kidney function is less than 10% of normal. At this point, the kidney function is so low that without dialysis or kidney transplantation, complications are multiple and severe, and death will occur from accumulation of fluids and waste products in the body. The most common cause of ESRD in the U.S. is diabetes.
Patients suffering from end stage renal disease typically undergo artificial dialysis of their blood, as a substitute to kidney transplantation. In the U.S. more than 400,000 people are on long-term dialysis and more than 20,000 have a functioning transplanted kidney.
Dialysis filters a patient's blood and rids the body of harmful wastes and extra salt and fluids. It also controls blood pressure and helps the body maintain the proper balance of chemicals such as potassium, sodium, and chloride.
Two common types of dialysis are employed, peritoneal dialysis and hemodialysis. In hemodialysis, the blood is filtered through an artificial kidney machine. Peritoneal dialysis uses a filtration process similar to hemodialysis, but the blood is filtered inside the body rather than by an external machine.
Hemodialysis is typically performed three times a week. Each treatment lasts from 2 to 4 hours and necessitates vascular access, typically to a major artery and a major vein of the patient.
There are three basic kinds of vascular accesses for hemodialysis, an arteriovenous (AV) fistula, an AV graft, and a venous catheter. A fistula is an opening or connection between any two parts of the body that are usually separate, for example, a hole in the tissue that normally separates the bladder from the bowel. While most kinds of fistula are a problem, an AV fistula is useful because it causes the vein to grow large and strong for easy access to the blood system. The AV fistula is considered the best long-term vascular access for hemodialysis because it provides adequate blood flow for dialysis, lasts a long time, and has a complication rate lower than the other access types. If an AV fistula cannot be created, an AV graft or venous catheter may be needed.
The current standard artificial vascular graft is fabricated from extruded expanded polytetrafluoroethylene (“ePTFE”). Such a ePTFE graft typically requires 2-4 weeks to mature following implantation and prior to initial use. Additionally, ePTFE grafts take 10-15 minutes to achieve hemostasis following puncture for hemodialysis. Another disadvantage with ePTFE vascular prostheses is suture-hole bleeding. This problem ahs been partially resolved by devising a special suture device (i.e. the “Goretex Suture”) whose suture is thicker than its introducing needle.
Several vascular access grafts have been devised in efforts of traversing sealing limitations inherent to vascular grafts. The VascuLink™, or Expedial™ produced by LeMaitre Vascular are two examples of such grafts. These devices are fabricated from enforced polycarbonate urethane foam. Although LeMaitre Vascular claims that these devices minimize suture hole bleeding, at present, clinical data demonstrating superior performance of these devices is unavailable.
A promising manufacturing technique of vascular prostheses is electrospinning.
Electrospinning creates a fine stream or jet of liquid that upon proper evaporation of a solvent or liquid to solid transition state yields a non-woven structure. The fine stream of liquid is produced by pulling a small amount of polymer solution through space by using electrical forces. More particularly, the electrospinning process involves the subjection of a liquefied substance, such as polymer, into an electric field, whereby the liquid is caused to produce fibers that are drawn by electric forces to an electrode, and are, in addition, subjected to a hardening procedure. In the case of liquid which is normally solid at room temperature, the hardening procedure may be mere cooling; however other procedures such as chemical hardening (polymerization) or evaporation of solvent may also be employed. The produced fibers are collected on a suitably located precipitation device and subsequently stripped therefrom. The sedimentation device is typically shaped in a desired geometry of the final product, which may be for example tubular in the case of vascular grafts.
The use of electrospinning for manufacturing or coating of vascular prostheses permits to obtain a wide range of fiber thickness (from tens of nanometers to tens of micrometers), achieves exceptional homogeneity, smoothness and desired porosity distribution along the coating thickness. When a graft includes an electrospun layer having a porous structure, such pores are invaded by cells and biologically active molecules from the region of the artery surrounding the graft.
The present inventors have previously demonstrated the advantages of using electrospinning for generating vascular grafts (see for example, International Patent Application, Publication Nos. WO 2002/049535, WO 2002/049536, WO 2002/049536, WO 2002/049678, WO 2002/074189, WO 2002/074190, WO 2002/074191, WO 2005/032400 and WO 2005/065578).
While reducing the present invention to practice and in efforts of improving self-sealing properties of vascular grafts the present inventors have devised a vascular graft which includes a layer impregnated or coated with a thrombogenic agent which substantially reduces bleeding from suture or needle access holes.